PURPOSE: To confirm the connection and parts defects of electric wires, by performing self-diagnosis by a diagnostic control circuit in accordance with a specified program on the basis of various input signals, when a start signal is transmitted.

CONSTITUTION: A lock control circuit 10 starts a 10sec timer when a main switch 21 is turned on, and puts in and off a key six times against a steering lock device and then a key-detection switch 13 generates six pulses. When the door lock is unlocked, an output is transmitted from the output terminal 10g. The door lock device is changed over to the locking state by an actuator 17. Next, the opened state of door, on-state of ACC switch 12, and actuation of memory storing a specified codes are checked and when these are normal, a buzzer 20 is actuated for a specified time from an output terminal 10k to inform of the normal actuation of the self-diagnosis. When it is judged that the codes in the radiowaves received through an antenna 15 coincides with the codes in memory, an output is transmitted from a specified terminal to the actuator in accordance with the signal.